In order to prevent leakage of an air from occurring and to keep the air pressure in a tire at a certain level, the inner surface of a pneumatic tire is provided with an inner liner layer mainly comprised of a butyl-based rubber having low gas permeability such as a butyl rubber and a halogenated butyl rubber. As the social requirement for energy saving increases in recent years, in order to reduce the automobile tire weight, many methods to reduce thickness of the gauge of this inner liner layer have been proposed. As a method to reduce thickness of the gauge of the inner liner layer, for example, an attempt is made to use a member, which is obtained by integrally bonding a butyl rubber sheet with an ethylene-vinyl alcohol copolymer film having an excellent gas barrier property, as the material for the inner liner layer (for example, see Patent Literature 1). In this case, for the foregoing bonding, an adhesive is used.
As to the inner liner layer of this pneumatic tire, a technology to make use of a film comprising a thermoplastic resin and a thermoplastic elastomer has been known. However, this film is insufficient in adhesion with a neighboring rubber layer.
Therefore, a technology such as to apply a pressure-sensitive adhesive to a film thereby adhering it with a neighboring rubber layer has been known. For adhesion of this film with the neighboring rubber layer, commercially available adhesives such as “Metaloc R-46” (manufactured by Toyokagaku Kenkyusho Co., Ltd.) and “Chemlok© 6250” (manufactured by LORD Corporation.) have been used in the past; however, these commercially available adhesives contain lead and halogen, so that development of an adhesive having a lower environmental burden has been desired. In addition, the tackiness of these adhesives is so low that there has been a problem that the tire cannot be produced stably.
On the other hand, as a technology to reduce the tire weight wherein an insulation layer, having an excellent adhesion property with a carcass cord as well as a significantly improved gas barrier property, is disposed between the inner liner layer and the carcass layer so as to reduce the rubber thickness of the inner liner layer thereby reducing the tire weight, a rubber composition to form an insulation layer of a pneumatic radial tire, wherein the insulation layer contains 1.5 to 4.5 parts by mass of sulfur relative to 100 parts by mass of a rubber component which comprises 20 to 70% by mass of an epoxidized natural rubber having the epoxidation rate of 3 to 50% by mol and a diene rubber as the remainder thereof, has been disclosed (for example, see Patent Literature 2).